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1. Measurement principle of the crystal oscillation dew point meter: By utilizing the property that the oscillation frequency changes when a crystal becomes wet, a crystal oscillation dew point meter can be designed. This is a relatively new technology that is still in an immature stage at present. There are similar products available abroad, but their precision is poor and their cost is high. 2. Measurement principle of semiconductor sensor dew point meters: Each water molecule has its own natural vibration frequency. When it enters the gaps in the semiconductor lattice, it resonates with the lattice that is charged and excited; this resonance frequency is proportional to the number of moles of water. The resonance of water molecules can cause semiconductors to emit free electrons, thereby increasing the electrical conductivity of the lattice and reducing its impedance. Semiconductor dew point meters designed using this feature can detect trace amounts of water at a dew point of -100°C. 3. Measurement principle of infrared dew point meters: By utilizing the property of water vapor in gases to absorb infrared light, infrared dew point meters can be designed. At present, it is difficult for this instrument to detect low dew points, mainly because the peak detection efficiency of the infrared detector is not yet sufficient to detect trace amounts of water absorption, and the presence of other components in the gas interferes with the absorption in the infrared spectrum. But this is a very new technology that holds great significance for the non-contact, online monitoring of moisture content in ambient gases.